Sex and speciation: molecular evolution of sexual dimorphism and mechanisms of speciation

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For many decades, the problem of speciation has been refractory to detailed genetic analyses, however with the availability of an increasing number of sequenced genomes, expression data and transgenic methodology, the scientific community is now in a position to understand the origins and evolution of species. During the last tenure of our NSERC grant, our studies were specifically directed towards understanding molecular evolution of sex- and reproduction-related genes and their role in speciation. We showed that genes involved in reproduction are evolving faster than genes with other functions, and that sexual function (male-/female-biased) and chromosomal location (sex vs. non-sex) are major factors influencing rapid gene evolution. Our goal in the next phase is to use modern molecular methodology to to test the hypothesis that variation and evolution of sexual system genes through their effects on sexual dimorphism are responsible for the development of reproductive isolation and speciation. Large scale gene expression studies of sterile interspecific hybrids have highlighted the importance of regulatory sequences in controlling gene expression and their role in speciation. We will analyse the evolution of cis-regularory sequences involved in sex-, tissue- and developmental stage-specific functions. Transgenics, using coding an regulatory sequences of different species for selected candidate genes will be done. Finally, with a view to link molecules to morphology and to unravel the dynamics of natural and sexual selection for a sexual a trait, we have undertaken a comprehensive study of the evolution of the male sexual trait, the sex combs, in Drosophila species. Studies involving artificial selection, behavioural experiments and gene expression profiles of selected lines will provide an understanding of the evolutionary dynamics of this sexual trait which has evolved rapidly and independently in different groups of Drosophila species. The results will shed light on the origins of species as well as on the evolution of sexual system genes and the tempo of change during speciation.